Mosquitoes get the ‘I’m full’ signal from their butts, not their brains

Mosquitoes have an appetite dampener in their derrières.

When mosquitoes’ bellies are full, special cells in their rectums block their bloodthirst, researchers report March 20 in Current Biology. The finding may unlock a way to stop the insects from biting in the first place. 

Female mosquitoes feed on blood to give their eggs a boost in protein and other nutrients before laying them. 

“We’ve known for decades that after the females take this big meal of blood, they almost completely turn off their attraction to find and bite humans,” says Laura B. Duvall, a neuroscientist at Columbia University. 

Researchers already knew a biochemical called neuropeptide Y, or NPY, influences feeding and feelings of fullness in a wide range of animals, including mosquitoes. Duvall and her colleagues previously found that disrupting a protein called NPY-like receptor 7 throughout mosquitoes’ bodies shut down NPY’s ability to quell hunger. The female mosquitoes kept trying to bite people, even with blood-bloated bellies. 

“We knew that this receptor was important, but we didn’t really know anything about how or where it was working in the mosquito,” Duvall says.

Duvall and her team genetically analyzed different sections of the dengue mosquito’s (Aedes aegypti) body, finding that the gene for receptor 7 was creating its product only in the very end of the gut.

“We found it in a really unexpected place,” Duvall says. Most of these kinds of receptors involved with appetite and fullness are found in the brain.

Using genetic manipulation, the team set the specific gut cells containing this receptor aglow with a fluorescent protein. Tagging the cells this way showed that there were special cells in pads in the rectum where the receptors were working. It’s these rectal pads that respond to the influence of appetite-altering neuropeptides. 

The rectal pads are close to nerve cells that release a chemical called RYamide after the mosquitoes feed. RYamide interacts with the rectal receptors, which then show an increase in calcium, much like a nerve cell. The cells also appear to release compounds similar to those used in nerve cell communication. Duvall and her team think the rectal cells act much like neurons, interpreting signals that the gut is full and relaying that message back to the brain. There are cells that behave similarly in mammalian guts, she says.

Medical entomologist Rebecca Johnson of the Connecticut Agricultural Experiment Station in New Haven is interested in seeing more research on how these rectal cells might influence the mosquitoes’ nervous systems. “This work indicates that mosquitoes are highly complex organisms,” she says.

Future research may reveal a chemical means to trigger the appetite-reducing effect in mosquitoes before they ever bite. Blunting their hunger may stymie the spread of dangerous mosquito-borne illnesses, especially because gut tissues loaded with receptors are much more accessible than the brain, Duvall says.

Current efforts to curb the insect’s activity include releasing genetically modified mosquitoes or targeting its sense of smell with repellents.

“Now you have a target that you can access by just feeding a compound to mosquitoes,” Duvall says.